The present invention concerns a series of sequential processes having for object to upgrade highly viscous heavy oils which cannot be transported under the usual conditions through pipe-lines as presently in operation. These heavy oils and more precisely these heavy curde oils are materials whose specific gravity is generally higher than 0.950 and whose viscosity at 70.degree. C. is close to or higher than 1000 centistokes (10.sup.-3 m.sup.2 /sec) or materials whose viscosity at 40.degree. C. is close to or higher than 10,000 centistokes (10.sup.-2 m.sup.2 /sec) such, for example, as the heavy crude oils from the Athabasca sands or the Orenoque belt. In addition to their high viscosity, these oils are also characterized by a high content of asphaltenes and a very low content of gasoline distilling below 200.degree. C. (or even below 100.degree. C.), particularly this is the case of the heavy crude oils produced in the petroleum fields of the Orenoque belt (these crude oils often do not contain substantially more than to 2% by weight of light gasoline).
In view of their high viscosity, these crude oils cannot be transported as such. Several solutions, already applied to conventional crude residues of high viscosity or to crude oils produced in very cold regions, may obviously be considered, such as a dilution with a light fluxing fluid and/or the maintenance of the oil in the pipe-line at a sufficient temperature to avoid pumping and conveyance problems. Another solution, also suggested, consists of proceeding at the oil well outlet to a minimum refining operation, so as to convert the considered crude oil and to extract therefrom the noble fraction which can be transported without problem. Thus a refining operation, comprising desalting, deasphalting with pentane and visbreaking of the deasphalted oil, provides only for the deasphalted oil, the viscosity required for its pipe-line transportation under at least substantially normal conditions, nonetheless, in this particular case, an unsolved problem is that raised by the asphaltenes present in the solid state which are difficult to transport and must be used to produce vapor or power on the very site of production. Another type of refining, comprising desalting and coking, also provides for the production, on the one hand, of a transportable distillate fraction and on the other hand, of a solid, i.e. coke which can be used, similarly as the asphaltenes in the preceding case, for producing vapor or power on the production field.